The idea of managing mobility of a wireless device or mobile station on a network has been around for some time. Allowing a mobile station (MS) such as a cell phone or a personal digital assistant (PDA) to roam on the wireless network requires managing various equipment. When a mobile station passes from one radio tower to another radio tower, the mobile station can pass into areas of the network controlled by different equipment, such as a packet data serving node (PDSN) and require a handoff.
With the advent of Internet Protocol (IP), networks began sending data in packets and using an IP address to route the data to its final destination. In time, wireless networks started to become data capable and would assign an IP address to a mobile station for the purpose of sending data to the mobile station. Generally, interconnection between devices is standardized to a certain degree based on the International Organization for Standardization (ISO)'s definition of a model for Open Systems Interconnection (OSI). OSI is used to define modes of interconnection between different components in networking systems and uses a seven layer model to do so.
Among the seven layers, Layer 3 (L3) is the network layer which is concerned with the delivery of packets of data. This layer defines the address structure of the network and how packets should be routed between end systems. IP and Internet Packet Exchange (IPX) are examples of network layer protocols. Layer 2 (L2) is the data link layer which also defines a lower level addressing structure for use between end systems as well as a lower level framing and checksums which are used to transmit data onto the physical medium. Ethernet, Token Ring, and Frame Relay are examples of data link layer or L2 protocols. Typically, L2 switching is implemented along side L3 routing for local area networks to facilitate communication between devices in a common IP subnet. However, in a wireless network where a mobile station can roam among base stations handoffs can pose a problem in terms of security and continuity of data flow.
Mobile IP was introduced to allow a mobile station to keep the same IP address regardless of where the mobile station travels. When the mobile station is at home, it is on the home network, or the network that it is typically associated with. The router connected to the home network is the home agent. When the mobile station is away from the home network, it associates with a foreign network and communicates through a foreign agent. In the event that packets are sent to a mobile station, the packets first travel to the home network. If the mobile station is not residing in the home network the packets are forwarded to the foreign agent with which the mobile station is registered. The packets are delivered to the mobile station from the foreign agent.
In a wireless IP network, an active session on a MS may incur inter-PDSN handoffs as the MS roams around the network. This may cause service disruption since re-negotiation of L2 and L3 protocols will occur between the mobile station and the network. Therefore, it would be desirable to mitigate these service disruptions during inter-PDSN handoffs of active sessions.